U.S. patent application number 10/445862 was filed with the patent office on 2004-04-15 for air circulation system.
This patent application is currently assigned to MESTEK, INC.. Invention is credited to Novak, Anthony C., Schneider, Stephen M..
Application Number | 20040072535 10/445862 |
Document ID | / |
Family ID | 31191191 |
Filed Date | 2004-04-15 |
United States Patent
Application |
20040072535 |
Kind Code |
A1 |
Schneider, Stephen M. ; et
al. |
April 15, 2004 |
Air circulation system
Abstract
An air circulation system for use with or without ductwork
having an outside air stream and a return air stream includes a
controller and a return damper apparatus operatively connecting the
return air stream to the controlled environment. The air
circulation system further includes a heating unit and an air mass
sensor disposed adjacent to the return damper apparatus. The air
mass sensor selectively and directly detecting a ventilation rate
of air moving through the return damper apparatus and communicates
the ventilation rate to the controller which selectively modulates
operation of the heating unit in dependence upon the ventilation
rate.
Inventors: |
Schneider, Stephen M.;
(Feeding Hills, MA) ; Novak, Anthony C.;
(Granville, MA) |
Correspondence
Address: |
Nicholas J. Tuccillo, Esq.
McCormick, Paulding & Huber LLP
185 Asylum Street, CityPlace II
Hartford
CT
06103
US
|
Assignee: |
MESTEK, INC.
Westfield
MA
|
Family ID: |
31191191 |
Appl. No.: |
10/445862 |
Filed: |
May 27, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60397216 |
Jul 19, 2002 |
|
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|
Current U.S.
Class: |
454/229 |
Current CPC
Class: |
F24F 2011/0002 20130101;
F24F 2110/40 20180101; F24F 11/0001 20130101; F24F 11/83
20180101 |
Class at
Publication: |
454/229 |
International
Class: |
F24F 007/06 |
Claims
What is claimed is:
1. An air circulation system for use with ductwork having an
outside air duct and a return air duct, said air circulation system
comprising: a controller; a return damper apparatus operatively
connecting said return air duct to said ductwork; a heating unit;
an air mass sensor for selectively and directly detecting a
ventilation rate of air moving through said return damper apparatus
and communicating said ventilation rate to said controller; and
wherein said controller selectively modulates operation of said
heating unit in dependence upon said ventilation rate.
2. The air circulation system according to claim 1, further
comprising: a discharge temperature sensor for detecting a
temperature of air discharged from said heating unit; and wherein
said controller selectively modulates operation of said heating
unit in dependence upon said ventilation rate and said discharged
air temperature.
3. The air circulation system according to claim 1, further
comprising: a temperature sensing means for determining an actual
temperature rise of air in said ductwork as said air moves from a
first location prior to said heating unit to a second location
after said heating unit; and wherein said controller selectively
modulates operation of said heating unit in dependence upon said
ventilation rate and said actual temperature rise.
4. The air circulation system according to claim 3, wherein: said
temperature means comprises an ambient temperature sensor for
detecting a temperature of air moving through said outside air
duct, a return temperature sensor for detecting a temperature of
air moving through said return air duct, and a discharge
temperature sensor for detecting a temperature of air discharged
from said heating unit; and wherein said ambient temperature sensor
and said return temperature sensor are each oriented prior to said
heating unit.
5. The air circulation system according to claim 1, wherein: said
air mass sensor is disposed adjacent to said return damper
apparatus and comprises an array of air pressure units each having
a plurality of apertures associated therewith for capturing a
portion of said air moving through said return damper apparatus, as
well as an amplification baffle oriented adjacent one of said
apertures; and said array of air pressure units are substantially
oriented in a grid pattern.
6. The air circulation system according to claim 5, wherein: said
heating unit comprises a direct-fired burner apparatus.
7. The air circulation system according to claim 1, wherein: said
air mass sensor repeats said direct detection of said ventilation
rate in accordance with one of a periodic schedule, an
environmental parameter and a command inputted to said
controller.
8. A method of controlling an air circulation system for ductwork
having an outside air duct, a return air duct and a heating unit,
said method comprising the steps of: orienting a return damper
apparatus to operatively connect said return air duct to said
ductwork; orienting an air mass sensor adjacent to said return
damper apparatus; selectively utilizing said air mass sensor to
directly detect a ventilation rate of air moving through said
return damper apparatus; and communicating said detected
ventilation rate to a controller of said air circulation system,
wherein said controller selectively modulates operation of said
heating unit in dependence upon said detected ventilation rate.
9. The method of controlling an air circulation system according to
claim 8, said method further comprising the steps of: detecting a
discharge temperature of air discharged from said heating unit; and
selectively modulating the operation of said heating unit in
dependence upon said detected ventilation rate and said discharge
temperature.
10. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of:
calculating an actual temperature rise of air in said ductwork as
said air moves from a first location prior to said heating unit to
a second location after said heating unit; and selectively
modulating the operation of said heating unit in dependence upon
said detected ventilation rate and said actual temperature
rise.
11. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of:
calculating said actual temperature rise utilizing data from an
ambient temperature sensor for detecting a temperature of air
moving through said outside air duct, a return temperature sensor
for detecting a temperature of air moving through said return air
duct, and a discharge temperature sensor for detecting a
temperature of air discharged from said heating unit.
12. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of: orienting
an outside damper apparatus to operatively connect said outside air
duct to said ductwork; and closing said outside damper apparatus
prior to detecting said detected ventilation rate.
13. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of:
determining when activation of said heating unit is requested for
said air circulation system; activating said heating unit when said
controller has determined that activation of said heating unit has
been requested, said controller permitting said activation only
when said activation does not conflict with said controller's
selective modulation of said heating unit in dependence upon said
detected ventilation rate.
14. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of: orienting
an outside damper apparatus to operatively connect said outside air
duct to said ductwork; selectively modulating operation of said
heating unit so as to maintain a predetermined ventilation rate;
determining whether said detected ventilation rate falls below said
predetermined ventilation rate; and modulating one of said return
damper apparatus and said outside damper apparatus when said
detected ventilation rate has been determined to have fallen below
said predetermined ventilation rate.
15. The method of controlling an air circulation system according
to claim 14, said method further comprising the steps of:
determining when modulation of one of said return damper apparatus
and said outside damper apparatus is requested to maintain a
predetermined internal building pressure; modulating one of said
return damper apparatus and said outside damper apparatus when said
controller has determined that modulation of one of said return
damper apparatus and said outside damper apparatus has been
requested to maintain a predetermined internal building pressure,
said controller permitting said modulation only when it has been
determined that said detected ventilation rate has not fallen below
said predetermined ventilation rate.
16. The method of controlling an air circulation system according
to claim 14, said method further comprising the steps of:
calculating an actual mixed air temperature of a combination of
said air moving through said return damper apparatus and said air
moving through said outside damper apparatus; determining when
modulation of one of said return damper apparatus and said outside
damper apparatus is requested to maintain a predetermined mixed air
temperature; and modulating one of said return damper apparatus and
said outside damper apparatus when said controller has determined
that modulation of one of said return damper apparatus and said
outside damper apparatus has been requested to maintain a
predetermined mixed air temperature, said controller permitting
said modulation only when it has been determined that said detected
ventilation rate has not fallen below said predetermined
ventilation rate.
17. The method of controlling an air circulation system according
to claim 14, said method further comprising the steps of:
determining when manual manipulation of said controller has been
initiated to modulate one of said return damper apparatus and said
outside damper apparatus; and modulating one of said return damper
apparatus and said outside damper apparatus when said controller
has determined that said manual manipulation has been initiated,
said controller permitting said modulation only when it has been
determined that said detected ventilation rate has not fallen below
said predetermined ventilation rate.
18. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of:
selectively modulating operation of said heating unit so as to
maintain a predetermined ventilation rate; determining whether said
detected ventilation rate falls below said predetermined
ventilation rate; and disabling said heating unit when said
detected ventilation rate has been determined to have fallen below
said predetermined ventilation rate for a predetermined time
period.
19. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of: utilizing
a direct-fired burner apparatus as an element of said heating
unit.
20. The method of controlling an air circulation system according
to claim 8, said method further comprising the steps of: repeating
said direct detection of said ventilation rate in accordance with
one of a periodic schedule, an environmental parameter and a
command inputted to said controller.
21. An air circulation system for managing an outside air stream
and a return air stream in a controlled environment, said air
circulation system comprising: a controller; a return damper
apparatus operatively connecting said return air stream to said
controlled environment; a heating unit; an air mass sensor for
selectively and directly detecting a ventilation rate of air moving
through said return damper apparatus and communicating said
ventilation rate to said controller; and wherein said controller
selectively modulates operation of said heating unit in dependence
upon said ventilation rate.
22. The air circulation system according to claim 21, further
comprising: a discharge temperature sensor for detecting a
temperature of air discharged from said heating unit; and wherein
said controller selectively modulates operation of said heating
unit in dependence upon said ventilation rate and said discharged
air temperature.
23. The air circulation system according to claim 21, further
comprising: a temperature sensing means for determining an actual
temperature rise of air in said environment as said air moves from
a first location prior to said heating unit to a second location
after said heating unit; and wherein said controller selectively
modulates operation of said heating unit in dependence upon said
ventilation rate and said actual temperature rise.
24. The air circulation system according to claim 23, wherein: said
temperature means comprises an ambient temperature sensor for
detecting a temperature of air in said outside air stream, a return
temperature sensor for detecting a temperature of air in said
return air stream, and a discharge temperature sensor for detecting
a temperature of air discharged from said heating unit; and wherein
said ambient temperature sensor and said return temperature sensor
are each oriented at a location prior to said heating unit.
25. The air circulation system according to claim 21, wherein: said
air mass sensor comprises an array of air pressure units each
having a plurality of apertures associated therewith for capturing
a portion of said air moving through said return damper apparatus,
as well as an amplification baffle oriented adjacent one of said
apertures; and said array of air pressure units are substantially
oriented in a grid pattern.
26. The air circulation system according to claim 25, wherein: said
heating unit comprises a direct-fired burner apparatus.
27. The air circulation system according to claim 21, wherein: said
air mass sensor repeats said direct detection of said ventilation
rate in accordance with one of a periodic schedule, an
environmental parameter and a command inputted to said
controller.
28. A method of controlling an air circulation system for managing
an outside air stream, a return air stream and a heating unit in a
controlled environment, said method comprising the steps of:
orienting a return damper apparatus to operatively connect said
return air stream to said controlled environment; orienting an air
mass sensor adjacent to said return damper apparatus; selectively
utilizing said air mass sensor to directly detect a ventilation
rate of air moving through said return damper apparatus; and
communicating said detected ventilation rate to a controller of
said air circulation system, wherein said controller selectively
modulates operation of said heating unit in dependence upon said
detected ventilation rate.
29. The method of controlling an air circulation system according
to claim 2, said method further comprising the steps of: detecting
a discharge temperature of air discharged from said heating unit;
and selectively modulating the operation of said heating unit in
dependence upon said detected ventilation rate and said discharge
temperature.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application Serial No. 60/397,216, filed on Jul. 19, 2002, herein
incorporated by reference in its entirety.
FIELD OF THE INVENTION
[0002] This invention relates in general to an air circulation
system, and deals more particularly with an air circulation system,
which controls the rise in temperature of the supply air stream
relative to the amount of recirculated air in the air circulation
system.
BACKGROUND OF THE INVENTION
[0003] Air circulation systems have become integral components in a
wide variety of building applications, both residential and
commercial. Typically, air circulation systems comprise a duct
system in combination with a fan or blower and enable the
selective, and oftentimes constant, recirculation of air. The
circulation, or recirculation, of air may be utilized to promote a
specific pressure regimen within the building, such as to provide a
positive building pressure, or may instead be utilized to assist in
the removal of harmful air-borne contaminants or to provide heating
or air conditioning to the building as a whole. Of course, air
circulation systems may be designed to accomplish one or more of
these objectives.
[0004] Heating components are typically utilized in conjunction
with air circulation systems to provide an influx of heat to the
recirculated air, upon demand, or as a function of the operation
parameters of the overall air circulation system.
[0005] Although many different types of heating components are
known, direct fired heating units are oftentimes utilized to
provide the necessary infusion of heat to an air circulation
system. Direct fired heating units typically utilize burners, or
the like, oriented in series with the duct system and act to
directly heat a circulated air mass as it passes through the
burner, the heated air mass being subsequently delivered to
selected portions of the building. Typically, these direct fired
heating units are fueled by natural gas or propane. These systems,
however, are somewhat problematic as the fuel utilized by a given
burner apparatus also inherently passes the by-products of
combustion into the air mass itself during the heating process,
thus leading to contamination concerns.
[0006] Several known air circulation systems have been designed to
address the contamination concerns inherent in the utilization of
direct fired burners. One type of known air circulation system
utilizes damper positioning sensing to determine the percentage of
recirculated air in the total air mass (known as the `ventilation
rate`), whereby the burner is controlled, in part, on the basis of
the determined ventilation rate and the permissible equivalent
temperature rise of the air mass before and after it has been
treated by the burner. These damper positioning sensing (`DPS`)
systems typically utilize sensors to determine the physical
position of louvers in the damper units which regulate the influx
of outside air, as well as for determining the physical position of
louvers in those damper units which regulate the influx of
recirculated air. By sensing the physical position of louvers in
each of the damper units, DPS systems can estimate how `open` each
damper unit is and thereby calculate the likely ventilation rate
for the system as a whole. DPS systems do not, therefore, directly
measure the air mass travelling through any of the damper units,
rather these systems rely upon an indirect method for determining
the air mass flow through each of the damper units in order to
calculate the ventilation rate and subsequent control of the burner
element.
[0007] As will be appreciated, the accuracy of DPS systems is
intimately dependent upon the accuracy of the sensors in
determining the actual, physical position of the louvers in the
damper units. Should there exist problems with the structural
integrity of the mechanical linkages in the damper units, or if
there are any other environmental or structural complications, the
sensors will misreport the actual position of the louvers, and
hence, determination of the air mass moving through each of the
damper units will be erroneously calculated. Moreover, the presence
of dirty or blocked filters within a DPS system may also cause a
miscalculation of the moving air mass, a miscalculation which DPS
systems are unable to detect or compensate for.
[0008] It will therefore be readily apparent that determining the
ventilation rate from the indirect sensing of an air mass moving
through a damper unit, as in known DPS systems, is susceptible to a
myriad of structural and environmental factors which detrimentally
affect the accuracy of the system as a whole. In addition, the
inaccuracy of DPS systems only tend to increase in magnitude the
longer the systems are in use.
[0009] Other known systems, such as CO.sub.2-based systems, exist
to address the contamination concerns of direct-fired systems,
however these systems also suffer from operational shortcomings due
to the detrimental effect that altitude and humidity, amongst other
environmental concerns, have on the accuracy of the system.
Moreover, CO.sub.2-based systems have inherently limited
measurement ranges which typically require large amounts of outside
air to be heated, thus raising operating and maintenance costs.
[0010] With the forgoing problems and concerns in mind, it is the
general object of the present invention to provide an air
circulation system which overcomes the above-described drawbacks
and which ensures that air flow measurements are accurately and
directly monitored in light of the temperature rise in the supply
air stream, thereby systematically controlling the harmful build-up
of combustion by-products in the circulating air mass.
SUMMARY OF THE INVENTION
[0011] It is an object of the present invention to provide an air
circulation system.
[0012] It is another object of the present invention to provide an
air circulation system which recirculates a selected portion of the
air within a building environment.
[0013] It is another object of the present invention to provide an
air circulation system which utilizes a direct-fired heating
unit.
[0014] It is another object of the present invention to provide an
air circulation system which effectively restricts the build-up of
combustion by-products to within a predetermined safety range.
[0015] It is another object of the present invention to provide an
air circulation system which effectively restricts the build-up of
combustion by-products to within a predetermined safety range by
limiting the allowable temperature rise through the system.
[0016] It is another object of the present invention to provide an
air circulation system which utilizes sensor arrays and an
automated controller to effectively restrict the build-up of
combustion by-products to within a predetermined safety range.
[0017] It is another object of the present invention to provide an
air circulation system which automatically and periodically
self-calibrates itself to ensure maximum efficiency and safety.
[0018] It is another object of the present invention to provide an
air circulation system which automatically and periodically
self-calibrates itself while accounting for current structural
conditions of the system.
[0019] It is another object of the present invention to provide an
air circulation system which is capable of parallel consideration
of different operational parameters.
[0020] It is another object of the present invention to provide an
air circulation system which is capable of prioritizing different
operational parameters.
[0021] These and other objectives of the present invention, and
their preferred embodiments, shall become clear by consideration of
the specification, claims and drawings taken as a whole.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIG. 1 is a schematic diagram illustrating an air
circulation system, according to one embodiment of the present
invention.
[0023] FIG. 2 illustrates an array of air pressure units integrated
with the air circulation system of FIG. 1.
[0024] FIG. 3 illustrates a pair of air pressure units mounted in
conjunction with an amplification baffle.
[0025] FIG. 4 is a partially cut-away illustration of the air
circulation system depicted in FIG. 1.
[0026] FIG. 5 is an operational flow diagram illustrating the
temperature detection, computation of ventilation rate and control
of the temperature rise in the air circulation system, according to
one embodiment of the present invention.
[0027] FIG. 6 is a damper control flow diagram for the air
circulation system.
[0028] FIG. 7 is a safety flow diagram for the air circulation
system.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] FIG. 1 is a schematic illustration of an air circulation
system 10, according to one embodiment of the present invention. As
shown in FIG. 1, the air circulation system 10 includes a
controller 12, a heating unit 14 and a return damper apparatus 16.
The heating unit 14 itself includes a gas valve 18, which
selectively regulates the influx of fuel, typically hydrocarbon
fuel or the like, to a burner component of the heating unit 14. In
this regard, one function of the controller 12 is to control the
operation of the gas valve 18, in accordance with either a manual
input, automatic control, or in relation to pre-set operational
parameters.
[0030] It will be readily appreciated that the controller 12 may be
comprised of either a manual input keyboard and display screen, or
an internalized computer and associated sub-routine, or both,
without departing from the broader aspects of the present
invention.
[0031] Returning to FIG. 1, an outside air-metering device 20 is
utilized to provide the air circulation system 10 with a variable
amount of `fresh` outside air (`0A`); that is, air which has not
previously circulated through the air circulation system 10. The
outside air-metering device 20 may be any type of known damper,
louver/damper apparatus or the like without departing from the
broader aspects of the present invention.
[0032] A plurality of sensor arrays are also shown in FIG. 1 and
serve to relate critical data concerning the temperature and volume
of the air mass being processed by the air circulation system 10,
at any given time, to the controller 12. Incoming air temperature
sensor 22, which may be a single sensor or, preferably, an array of
individual sensors, is oriented along an outside air duct 24 and
monitors the temperature of the incoming air provided to the
outside air-metering device 20. Returning air temperature sensor
26, which may be a single sensor or, preferably, an array of
individual sensors, is oriented along a return duct 28 and monitors
the temperature of the recirculated air provided to the return
damper apparatus 16.
[0033] Oriented before the return damper apparatus 16 and the
heating unit 14 is an air pressure sensor 30. The air pressure
sensor 30 is preferably utilized to monitor pressure of the return
air mass provided to the heating unit 14 and employs pressure
transducers or the like to convert the detected air pressure to an
electrical signal indicative of the return air mass which is
provided to the heating unit 14. In addition, a discharge air
temperature sensor 31 is disposed downstream of the heating unit 14
and serves to monitor the discharge air temperature of the air mass
leaving the heating unit 14. Both the air pressure sensor 30 and
the temperature sensor 31 may be comprised of a single sensor or,
preferably, an array of individual sensors without departing from
the broader aspects of the present invention.
[0034] The air pressure sensor 30 of FIG. 1 is preferably
constructed as an array of operatively connected air pressure units
32 which are oriented in a grid pattern, shown in FIG. 2, thereby
enabling the air pressure units 32 to receive, in aggregate, an
accurate and direct detection of the air mass moving through the
return duct 28 at any given time. The air pressure units 32 include
a plurality of detection apertures 33 formed in substantially
hollow tubes, into which the moving air mass is incident. Moreover,
the air pressure units 32 are integrated with one another via
substantially hollow collection tubes 34, depicted most clearly in
FIG. 3, which themselves are channeled into substantially hollow
manifold tubes 36.
[0035] The information detected by the air pressure units 32 is
subsequently communicated by the manifold tubes 36 to the
controller 12 after the appropriate signal interpretation, via
pressure transducers or the like, has occurred. As will be
appreciated, by utilizing the air pressure units 32, and the
associated substantially hollow tubing, the present invention may
accurately and passively record the air flow through the return
duct 28 without employing any moving parts, thus reducing the
incident of mechanical wear and failure and the associated
maintenance and replacement costs.
[0036] As further shown in FIG. 3, the air pressure units 32 may be
selectively coupled to an amplifying baffle 38 in order to provide
accurate readings even when the volume of the circulating air mass
is relatively low. That is, the amplifying baffle 38 serves to
create turbulence in the movement of even a small amount of air
adjacent the detection apertures 33 as the air moves through the
return duct 28, thereby enabling the detection apertures 33 to
capture and record such air mass movement.
[0037] The air pressure units 32 are preferably spaced every 6 to
12 inches over the entire face of the return duct 28 in order to
obtain an accurate measurement. Moreover, the volume of the air
mass detected by each of the air pressure units 32 in the sensor
array 30 are averaged, conditioned and interpreted by the
controller 12 to calculate the ventilation rate of the air
circulation system 10. As will be appreciated, by employing
multiple velocity pressure sensor points, in the form of the array
of air pressure units 32, the present invention ensures a highly
accurate measurement of the total airflow through the return duct
28.
[0038] It is therefore an important aspect of the present invention
that the volume of the air mass moving through the return duct 28
is directly calculated via the air pressure units 32, in stark
contrast to the DPS and C0.sub.2 systems previously discussed which
utilize indirect calculation and determination of the moving air
mass. It will be readily appreciated that by directly sensing the
volume of the air mass moving through the return duct 28, the air
circulation system 10 returns highly accurate measurements to the
controller 12, thus resulting in highly accurate ventilation rates
for use in controlling the burner 14, as will be discussed in more
detail later. Indeed, laboratory analysis of the sensor array 30
has proven that the direct measurement of the air mass moving
through the return duct 28 at any given time to be extremely
repeatable and accurate to within 4%.
[0039] It is another important aspect of the present invention that
the automatic self-calibration function of the air circulation
system 10 is independent of the structural integrity of the air
circulation system 10 in providing accurate measurements upon which
to base future decisions regarding operation and modulation of the
burner component of the heating unit 14, as well as the damper
apparatuses 16/20. Thus, the air circulation system 10 of the
present invention ensures that the controller 12 is capable of
accurately monitoring the composite airflows within the air
circulation system 10 regardless of the presence of dirty filters,
broken damper linkages, or the like. In this regard, the automatic
self-calibration function of the air circulation system 10 is
highly adaptive to any changes in the overall system, while also
being capable of compensating for any such changes automatically
with each self-calibrating operation.
[0040] Another important aspect of the present invention is that
the air circulation system 10 may be selectively controlled so as
to initiate a self-calibration operation on a set timetable, such
as but not limited to once a day or month, or rather in response to
environmental criteria, such as but not limited to the inside air
temperature, the outside air temperature, or the difference between
the two.
[0041] Indeed, the present invention achieves its high accuracy at
least in part due to the ability of the air circulation system 10
to self-calibrate itself at a time period after installation, as
opposed to being calibrated in the factory or lab prior to
installation, thus avoiding the need for the application of
corrective factors or routines.
[0042] It is another important aspect of the present invention that
the air circulation system 10 is capable of maintaining highly
accurate measurements of the air mass moving through the return
duct 28 even when the air mass is extremely small in magnitude, via
the employment of the amplifying baffles 38, as best seen in FIG.
3. Such an ability renders the present invention especially
applicable to those situations where installation in low ambient
pressure environments is desired.
[0043] The operation of the air circulation system 10 will now be
generally described in conjunction with a partially cut-away
illustration of the air circulation system 10 depicted in FIG. 4
and the operational flow diagram of FIG. 5. As shown in FIG. 4, the
air circulation system 10 controls the temperature rise between the
air mass entering the heating air unit 14 and air mass leaving the
heating unit 14, relative to the amount of recirculated air, that
is, the ventilation rate, provided to the return damper apparatus
16, by selectively attenuating or closing the gas valve 18, as will
be described hereinafter.
[0044] At the first stage of operation, the air circulation system
10 must self-calibrate itself in order to have a base line against
which the subsequent readings of the various sensor arrays may be
compared. At the initiation of the self-calibration routine, as
shown in the operational flow diagram of FIG. 5, it is decided in
step 40 whether the self-calibration routine is scheduled. If `no`,
then the controller 12 does not perform the self-calibration and,
if `yes`, the controller 12 permits the self-calibration routine to
continue. Although the air circulation system 10 has been described
utilizing a scheduled self-calibration operation, the present
invention is not so limited in this regard as the self-calibration
operation may be repeatedly performed on a daily or weekly basis,
as automatically scheduled in advance, or in relation to
predetermined changes in temperature fluctuations, weather
conditions or other design criteria without departing from the
broader aspects of the present invention.
[0045] Returning to FIGS. 4 and 5, after the controller 12 has
determined that the self-calibration should continue, it is
necessary to isolate the air circulation system 10 from the outside
air in order to obtain a base reading so as to calculate the
ventilation rate of the air circulation system 10 in the future. In
step 42, therefore, the controller 12 drives the outside
air-metering device 20 to completely shut off the supply of outside
air from the air circulation system 10, while in step 44 the return
damper apparatus 16 is driven to its fully open position, thus
ensuring that 100% of the air mass moving through the air
circulation system 10 is recirculated air. In addition, although
not represented in FIG. 5, the controller will also ensure both
that the heating unit 14 is off, and that the blower 45 is on. A
predetermined time delay is then instituted in step 46 to allow the
air circulation system 10 to stabilize. A time of delay of a few
minutes, preferably 3-5 minutes, is typically employed, however the
time delay may be adjusted in conformance with the size, and type,
of ductwork involved without departing from the broader aspects of
the present invention.
[0046] Once the time delay of step 46 has expired, the air pressure
sensor 30 communicates the volume of the air mass moving through
the return duct 28 to the controller 12 where these values are then
averaged, conditioned and interpreted in step 48 by the controller
12 to determine a peak airflow signal at a 100% ventilation rate.
This peak airflow signal (P.sub.peak) is stored by the controller
12 as a constant and is utilized during operation of the air
circulation system 10 to determine the operating ventilation rate,
as will be described in more detail later. The return damper
apparatus 16 and the outside air-metering device 20 will then be
returned to their normal state of operation. By comparing the
output from the air pressure sensor 30 at the time of
self-calibration, with the output of the air pressure sensor 30
during those times when the dampers in the return damper apparatus
16 are operating normally, the controller 12 is able to accurately
compute, and control, the ventilation rate of the system 10; that
is, the controller 12 is able to accurately compute, and control,
the percentage of recirculated air to the total air mass moving
through the air circulation system 10.
[0047] Therefore, assuming: %RA=percent of return air (ventilation
rate);
[0048] %OA=percent of outside air;
[0049] P.sub.peak=stored peak airflow value; and
[0050] P.sub.actual=output of sensor 30 during normal operation.
The controller 12 may then calculate the actual ventilation rate of
the air circulation system 10 at any time utilizing the
equation:
%RA={square root}(P.sub.actual/P.sub.peak)*100.
[0051] As will be appreciated, the controller 12 can then calculate
the actual percent of outside air at any time utilizing the
equation:
%OA=100-%RA.
[0052] Returning to FIG. 5, step 50 represents the calculation of
the mixed air temperature of the air mass in area 51 of the air
circulation system 10, prior to treatment of the mixed air mass by
the heating unit 14. As depicted at step 50, the controller 12
utilizes information from the incoming air temperature sensor 22
and the returning air temperature sensor 26, in conjunction with
the previously determined ventilation rate (%RA) to calculate the
mixed air temperature (MAt) of the air mass in area 51 as
follows:
MAt=((OAt*%OA)/100)+((RAt*%RA)/100);
[0053] where OAt=outside air temperature (from sensor 22); and
[0054] RAt=return air temperature (from sensor 26).
[0055] As alluded to previously, an important aspect of the present
invention is for the controller 12 to control the operation of the
heating unit 14 such that, in light of a directly detected
ventilation rate (%RA), concentrations of post-combustion
contaminants are not permitted to exist in the air stream of the
air circulation system 10 in levels that would exceed manufacturer,
industry, or governmental standards. It is therefore vital that the
controller 12 first calculate the mixed air temperature (MAt) as
discussed above. It is also necessary for the controller 12 in step
52 to calculate the maximum equivalent temperature rise
(MaxEQ.DELTA.T); that is, for a given ventilation rate (%RA), it is
necessary to calculate the maximum equivalent temperature rise of
the mixed air mass as it moves from its position prior to the
heating unit 14 in area 51, to that portion of the air circulation
system 10 after the heating unit 14, as follows:
[0056] MaxEQ.DELTA.T=(%OA*50)/(19.63*K); where K is the gas
constant of the fuel utilized by the heating unit 14.
[0057] Utilizing, then, the values previously calculated as
discussed above, the controller 12 then calculates the maximum
discharge air temperature (MaxDAt) in step 54, as follows:
MaxDAt=MAt+MaxEQ.DELTA.T.
[0058] As its name suggests, the maximum discharge air temperature
(MaxDAt) is that temperature which the air mass leaving the heating
unit 14 must not exceed, taking in consideration the specific mixed
air temperature (MAt) and the directly detected ventilation rate
(%RA) of the air circulation system 10 at any given time. It is now
left to the controller 12, in step 56, to compare the maximum
discharge air temperature (MaxDAt) with the discharge air
temperature (DAt) as reflected by the value of the discharge air
temperature sensor 31.
[0059] As shown in FIG. 5, the controller 12 outputs one of two
possible commands in step 56 to the gas valve 18 where, in step 57,
the controller 12 causes the gas valve 18 to shut off, or otherwise
modulate, the supply of fuel to the heating unit 14 if the
discharge air temperature (DAt) is greater than the maximum
discharge air temperature (MaxDAt).
[0060] It is therefore an important aspect of the present invention
that the controller 12 is capable of directly monitoring the actual
ventilation rate of the air circulation system 10 and is thereby
capable of ascertaining if the discharge air temperature (DAt) is
impermissibly greater than the maximum discharge air temperature
(MaxDAt) given the detected ventilation rate. That is, the air
circulation system 10 of the present invention directly monitors
the operating parameters of the system 10 to ensure that a harmful
concentration of post-combustion contaminants is never permitted to
exist in the air stream of the air circulation system 10.
[0061] While the controller 12 may selectively modulate the gas
valve 18 if the discharge air temperature (DAt) is impermissibly
greater than the maximum discharge air temperature (MaxDAt), the
present invention also contemplates controlling the heating unit 14
in accordance with other salient operating parameters. As shown in
FIG. 5, the controller 12 also calculates, in step 58, the actual
equivalent temperature rise (ActEQ.DELTA.T); that is, for a given
ventilation rate (%RA), it is necessary to calculate the actual
equivalent temperature rise of the mixed air mass as it moves from
its position prior to the heating unit 14 in area 51, to that
portion of the air circulation system 10 after the heating unit 14,
as follows:
[0062] ActEQ.DELTA.T=[((%OA*(DAt-OAt))/100]+[((%RA*(DAt-RAt))/100];
where
[0063] DAt is the discharge air temperature value from sensor 31,
OAt is the outside air temperature value from sensor 22, and RAt is
the air temperature value from sensor 26.
[0064] Should the controller 12 determine, in step 56, that the
actual equivalent temperature rise (ActEQ.DELTA.T) exceeds the
maximum equivalent temperature rise (MaxEQ.DELTA.T), the controller
12 will output an appropriate command, in step 57, to the gas valve
18 thereby shutting off, or otherwise modulating the gas-firing
rate, the supply of fuel to the heating unit 14. As will be
appreciated, the permissible maximum temperature rise as dictated
by the ratio of the recirculated air mass to the outside air mass
will be stored in the memory of the controller 12 and may be
manually entered or, alternatively, may be fashioned to meet
industry or governmental standards, such as but not limited to ANSI
regulation Z83.18.
[0065] It is therefore another important aspect of the present
invention that the air circulation system 10 will, in a preferred
embodiment, issue a command to the gas valve to shut off the supply
of fuel to the heating unit 14, if: 1) The discharge air
temperature (DAt) exceeds the calculated maximum discharge air
temperature (MaxDAt) for a directly measured ventilation rate; or
2) The actual equivalent temperature rise (ActEQ.DELTA.T) exceeds
the maximum equivalent temperature rise (MaxEQ.DELTA.T) for a
directly measured ventilation rate. As considered hereinafter,
these conditions may be collectively referred to as the Ventilation
Control parameters for the air circulation system 10.
[0066] Another important aspect of the present invention is the
parallel consideration by the controller 12 of additional factors
surrounding the operation of the heating unit 14. Returning to FIG.
5, it can be seen that step 60 indicates if there exists a call for
heat, via an automatic thermostat or the like, in the environment
serviced by the air circulation system 10. If so, and in addition
to the calculation of the various parameters discussed previously,
the controller 12 will also look to a space temperature set point,
in step 62, to determine what specific temperature must be
achieved. The controller 12 then determines, in step 64, if the
temperature set point detected in step 62 is greater than the
discharge air temperature (DAt). If not, the controller 12 passes a
signal to step 56 indicating that the gas valve 18 should be
modulated to increase the heating capacity of the heating unit 14.
It should be noted, however, that the command from the controller
12 to increase the heating capacity of the heating unit 14, when
such an action is indicated by the determination in step 64, is
conditional upon the status of the Ventilation Control parameters,
as will be explained below.
[0067] As indicated earlier, the air circulation system 10 of the
present invention directly monitors the operating parameters of the
system 10 to ensure that a harmful concentration of post-combustion
contaminants are never permitted to exist in the air stream of the
air circulation system 10. In this regard, it is another important
aspect of the present invention that the controller 12 prioritizes
its determination of the Ventilation Control parameters over any
call for heat which may be issued in step 60 or any determination
in step 64. Thus, the controller 12 of the present invention
ensures that the gas valve 18 will not supply the heating unit 14
with fuel should the Ventilation Control parameters indicate that
the air circulation system 10 is exceeding its post-combustion
guidelines, even when the call for heat in step 60 and the
determination in step 64 request actions to the contrary.
[0068] It is therefore another important aspect of the present
invention that the controller 12 does not permit calls for heat,
which may be either manually or automatically initiated, to take
precedence over the safety concerns embodied by any regulatory
limits upon which the operation of the air circulation system 10
may be based.
[0069] In the preferred embodiment of the present invention, a
predetermined minimum ventilation rate may be maintained. That is,
the preferred embodiment of the present invention is operable to
maintain an influx of a predetermined percentage of outside air in
the total airflow being circulated through the air circulation
system 10. Moreover, the preferred embodiment of the present
invention permits at least three options, at the discretion of the
operator of the controller 12, for controlling the damper elements
of both the return damper apparatus 16 and the outside air metering
device 20 in order to selectively vary the ventilation rate.
[0070] In particular, an operator may instruct the controller 12
to:
[0071] 1) Automatically control the ventilation rate (%RA) in
accordance with maintaining building pressure. With this control
regimen, a pressure transducer, or the like, may be mounted in a
suitable location for measuring the pressure inside the building in
relation to the pressure outside the building. The damper elements
of both the return damper apparatus 16 and the outside air metering
device 20 may then be automatically positioned by the controller 12
to maintain a building pressure set-point entered into the
controller 12 by the operator;
[0072] 2) Manually control the ventilation rate (%RA) by manually
positioning the damper elements of both the return damper apparatus
16 and the outside air metering device 20 to an arbitrary position
as selected by the operator; and
[0073] 3) Automatically control the ventilation rate (%RA) in
accordance with a mixed air temperature set point. With this
control regimen, the damper elements of both the return damper
apparatus 16 and the outside air metering device 20 may be
automatically positioned by the controller 12 to maintain a
predetermined mixed air temperature (MAt), as calculated by the
controller 12.
[0074] FIG. 6 is a damper control flow diagram for the air
circulation system 10 which illustrates the control of the damper
elements of both the return damper apparatus 16 and the outside air
metering device 20 for each of the preceding three control
regimens. As shown in FIG. 6, the controller 12 first determines if
the blower 45 is running in step 70. If so, the controller 12
monitors parallel command architectures to determine the proper
adjustment of the damper elements of both the return damper
apparatus 16 and the outside air metering device 20.
[0075] One branch of the command architecture illustrated in FIG. 6
involves the controller 12 determining, in step 72, a predetermined
ventilation rate set point. The ventilation rate set-point may be
selected, for example, to be 20%, however it should be readily
appreciated that any predetermined ventilation rate may be
alternatively selected without departing from the broader aspects
of the present invention.
[0076] The controller 12 next determines, in step 74, the actual
ventilation rate (%RA) in accordance with the equation for the
same, as discussed previously in conjunction with FIG. 5. Step 76
reflects the controller 12 determining if the actual ventilation
rate is lower than the ventilation rate set point. If so, a command
is issued to suitably adjust the damper elements, in step 78, of
both the return damper apparatus 16 and the outside air metering
device 20 to bring the ventilation rate back above the ventilation
rate set-point.
[0077] In concert with the processing of this first branch, the
other branch of the command architecture illustrated in FIG. 6
involves the controller 12 determining, in step 80, which one of
the three control regimens have been selected by an operator.
Regardless of the control regimen selected, the controller 12 next
determines, in step 82, the actual value of the specific criteria
utilized by each of the control regimens. That is, in step 82, the
controller 12 determines what the actual building pressure is, what
position the dampers have been manually set to and the
corresponding ventilation rate, or what the actual mixed air
temperature is, in dependence upon the control regimen selected by
the operator. Step 76 again reflects a determination by the
controller 12 as to whether the specific criteria expressed by the
selection of a specific control regimen has been met. A command is
then issued to suitably adjust the damper elements, in step 78, of
both the return damper apparatus 16 and the outside air metering
device 20 to bring the specific criteria of the selected control
regimen in line with its predetermined value.
[0078] Similar to the parallel practice of the controller 12
previously discussed in conjunction with FIG. 5, it is another
important aspect of the present invention that the controller 12
prioritizes its determination of the ventilation rate set-point, in
step 72, over any of the control regimens expressed in step 80 or
any associated determination in step 76. Thus, the controller 12 of
the present invention ensures that any predetermined ventilation
rate set-point is maintained, even when a particular control
regimen has been selected in step 80 which may otherwise wish to
control the damper elements differently.
[0079] In addition to controlling the damper elements of both the
return damper apparatus 16 and the outside air metering device 20,
in accordance with a ventilation rate set-point or another control
regimen, the controller 12 of the present invention may also be
adapted to shut down the burner component of the heating unit 14 if
the ventilation rate is below a predetermined ventilation rate
set-point for a predetermined period of time. FIG. 7 illustrates a
predetermined ventilation rate set point in step 90, whereas the
actual ventilation rate is continually monitored by the controller
12. The controller 12 determines, in step 92, whether the actual
ventilation rate has been below the predetermined ventilation rate
set point for more than, in this instance, 3 minutes. If so, the
controller 12 issues a command to the heating unit 14 to shut down
the burner and re-set the system. It will be appreciated that the
specific values for the predetermined ventilation rate set-point
expressed in step 90, and the predetermined time period utilized by
the controller 12 in step 92, may be
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